Measurement of body fat in humans is one of the factors in checking the fitness and general health level of humans. Excess fat is known to be a risk factor with regard to heart disease, diabetes, and even cancer of certain kinds. Excess fat has recently come under a high degree of scrutiny by the health industry, and it is desirable to be able to make an accurate measurement of body fat in order to assess health risks.
Obesity is currently defined by a “body mass index” or BMI. A BMI of more than 27, according to Health Canada guidelines, is regarded as obese. However, recent reports suggest that the use of the BMI alone leads to two common forms of misclassification. The first is of a highly muscular individual with a high BMI who may be classified as “overfat”, when, in fact he/she is not. The second is of individuals with a healthy BMI (18.5 to 24.9) who actually do have an elevated body fat content and are at risk.
Another method for classifying body fat content is the density measurement. The percent body fat is calculated by an equation based on the density of the body. The density of the body is calculated by an equation that involves measuring a person suspended on a trapeze in the air, and then weighing the same person under water.
The equipment used for this measurement includes a special weigh scale, and a submersion pool or tank. Some of the drawbacks of this system are that the standard body density used for comparison is that of a young Caucasian. Modifications in the equations may be necessary for persons of other ethnic origins. In addition, some people feel uncomfortable when they must be fully submerged, leading to incorrect readings, the procedure requires a trained operator, and there is always air left in the lungs, and it is difficult to correct for this residual air accurately.
To date the usual and the cheapest method of fat measurement is conducted by a pair of calipers. The ends of the calipers are simply squeezed against a fold of the skin, at certain selected locations on the body. This system gives variable and erratic results, and is known to be unsatisfactory.
Systems for measurement of body fat have been proposed using near infrared light. One such proposal is described in experimental form in “A New Approach for the Estimation of Body Composition: Infrared Interactance”, by Conway J et al, American Journal of Clinical Nutrition 40: December 1984, pages 1123 to 1130. Systems have been proposed in patent literature using near infrared light. One such system is described in U.S. Pat. No. 4,928,014, R D Rosenthal, dated May 22, 1990.
This system was later found to be unsatisfactory and unreliable.
Another system for the measurement of body fat is the system known as magnetic resonance imaging (MRI). This system provides much more accurate results than any other system known, at present. However, the equipment is a major investment, in the order of millions of dollars. The operation of it requires a highly trained team of medical assistants. The entire system takes a relatively long time to scan a person. As a result the per person costs of MRI are too high to enable it to be used simply for body fat measurement.
Another system is the Deuterium Oxide Dilution system, but this is also a technical and demanding system, and is not satisfactory for use in every day medical practice, or in fitness testing.
However, when a doctor is carrying out a physical exam of a person, which may be required for insurance, or for admission to certain types of employment, or which may be required by the individual for an annual monitoring of health, some form of measurement of fat content is usually carried out, as part of the overall tests used to evaluate the state of health of the individual.
Consequently, even though it is well known to be inaccurate, the standard test for evaluating the fat content of the human body has, for many years, been the skin fold caliper test.
There are three distinct categories for human fat. These are structural, metabolic and storage fats. Structural fats form part of each and every cell of the body, mainly in the cell membrane. Metabolic fats are a group of lipids that are used in metabolic processes. Storage fats represent the largest component of human fat. Part of the storage fat is found in the subcutaneous layer of the skin which is the third layer of skin found beneath the epidermis and dermis layers. The remaining smaller part of storage fat is used as a cushion for the visceral organs (liver, heart, kidneys, etc.).
There are several different types of fat found in the human body. Some occur naturally, others are only attainable by diet. Briefly, the types of fat are saturated fats, unsaturated fats, phospholipids and triglycerides.
Saturated fats are commonly found in animal fat products such as butter, lard and animal meats. Unsaturated fats, are divided into two groups, mono or poly unsaturated fats. An example of a monounsaturated fat is Oleic acid and can be found in olive oil. Polyunsaturated fats are essential fatty acids and are only attainable through diet. Examples of polyunsaturated fats are linoleic acid, linolenic and arachidonic acids. These are essential fatty acids and may be found in soy bean oil, peanut oil and corn oil to name a few.
Phospholipid, the most common of which is lecithin, is an important common component of all cell membranes.
Triglycerides, composed of three fatty acids attached to glycerol molecule and are the storage form of fat that occurs when humans eat calories in excess of their energy needs.
In the case of cattle carcasses, fat content has been measured in the carcass of the dead animal using a needle probe inserted into the carcass. This system has given satisfactory results. However, it is of use only after the animal has been slaughtered. Clearly it is of no use to humans. Even for animals, it gave a reading which was after the fact. By the time the measurement was available, it was then too late to make any attempt to correct the fat content of the animal by altering the diet. Fat content of animal carcasses is a major factor in the price for the carcasses received by the farmer. Market considerations require the carcass to have a low fat content. If the fat content is excessive then the farmer will receive less for the animals than if the fat content is lower.
Where animals are being raised for slaughter it would be preferable to be able to monitor the fat content of the animals in-vivo as they were being raised. If testing were available in-vivo the animals diet could be adjusted to maintain a desirable low fat content. However measurement of animal fat content, while the animal is alive, cannot be done with the invasive, needle probe type of measurement system.
Near Infrared (NIR) Spectroscopy, with its non-invasive, in-vivo capabilities can solve this problem. It is useful in examining aqueous solutions and mixtures, as well as biological studies. The interest in near infrared spectroscopy, for the analysis of chemicals, stems from a number of factors. Absorptions in the near infrared region arise from vibrational transitions to the second or higher energy states. Because of the very low probability of such transitions, absorption intensities are several orders of magnitude below those of the corresponding fundamental vibrations in the infrared and/or ultraviolet (UV) region of optical spectrum. Consequently infrared is not as sensitive in analysis of species present at low concentrations. Additionally, near infrared spectroscopy has the advantage that aqueous solutions can be readily analyzed without much interference from water absorption.
The intense absorption of near infrared wavelengths, by a species, also allows them to penetrate a sample sufficiently to be useful in the analysis of thicker samples, such as body tissue.
The use of light in the near infrared region of light spectrum for purposes of analysing for certain chemicals or for creating “images” is discussed in U.S. Pat. No. 5,440,388, R Erickson, dated Aug. 8, 1995. In this patent, there are descriptions of numerous different types of technology, all of which are mentioned incidentally, in passing. The actual invention described relates to a piece of equipment in which there are a plurality of discrete light sources each producing monochromatic light of a specific wavelength, the light sources being combined into a single beam of light. An interferometer modulates the light beam and a detector detects each of the discrete wavelengths. This is different than using Fourier Transform Near Infrared (FT-NIR) Spectroscopy. The FT-NIR instrument makes use of an interferometer to encode data from the whole spectral range simultaneously. The Michelson interferometer is used to produce a signal of a lower frequency than the frequency emitted from the NIR source. The lower frequency contains the same information as the original radiation signal, but is converted to a speed slow enough for detection by a detector. The output of the interferometer is an interferogram of all wavelengths emitted by the source. A computer then performs the Fast Fourier Transform of the interferogram and results in a frequency domain trace.
Fourier Transform Near Infrared Spectroscopy has certain advantages over traditional spectroscopy, in which the response of a sample to light is measured by scanning sequentially over a range of wavelengths. Fourier Transform Near Infrared Spectroscopy measures the response of the sample to all the wavelengths of interest simultaneously, by measuring the light after it interacts with the sample and recording the entire spectrum at once.
In the description of '388, it is stated that for various different samples, the light sources will have to be changed and the detectors will also have to be changed. This system is an array of light sources of specific wavelengths and an array of detectors for detecting such wavelengths. The system must therefore be specified for the particular chemical being analysed, or the nature of the specific sample being imaged.
The system described in '388 is not suitable for measurement of body fat because it does not provide any details on its resolution or accuracy or its ability for chemical analysis. This is different than using FT-NIR spectroscopy. The FT-NIR spectrometer, which, by contrast, makes use of an interferometer to encode data from the whole spectral range simultaneously. The description of '388 is focussed on imaging rather than chemical composition of the material. There is one statement in the description of '388 which appears to be inaccurate, where it speaks of;
“Near infrared spectroscopy was applied to human skin in the 1950's, and has since been developed for transcutaneous measurements of body fat composition.”
There is no reference in the description for this assertion. In spite of a careful search of the literature, no such reference can be found.
It is desirable to provide a method of measurement of fat content of a body, whether human or animal, which is simple, accurate, and economical and which is non-invasive, and can be carried out in-vivo quickly, with lower cost equipment and with a minimum of training.